Unsteady Aerodynamic Characteristics of a Transonic Oscillating Cascade with Flow Separation

通过一系列的实验和数值模拟，研究了每片叶片吸力面上存在流动分离区的振荡叶栅的非定常气动特性。采用亚音速压气机叶栅和跨音速涡轮叶栅作为模型实例。实验中，采用影响系数法测量作用在叶片上的非定常气动力。利用附着在叶片表面的热膜传感器的输出信号检测叶片边界层的行为。从压气机叶栅的实验结果可以清楚地看出分离泡在振动叶片上的非定常行为，揭示了分离泡对非定常气动力I力矩的影响。在跨音速涡轮的实验中，发现激波振荡对叶片振动的影响是非常重要的。激波与边界层的相互作用导致吸力面边界层的快速发展和边界层的分离。在低频振荡的情况下，检测到叶片振荡的显著不稳定性。采用TVD格式对含Baldwin-Lomax湍流模型的二维Navier-Stokes方程进行求解，提出了一种叶片绕动非定常流场的数值计算方法。通过与已有实验数据的比较，验证了该方法的有效性。在无粘流动假设下，对跨声速涡轮进行了数值模拟。结合数值结果，对实验中发现的振动失稳机理进行了详细的研究。结果表明，叶片吸力面冲击点附近的显著相变是导致叶片失稳的主要因素。

The unsteady aerodynamic characteristics of oscillating cascades, in which each blade accompanied a flow separation region on its suction surface, were studied by a series of experiment and numerical simulation. A subsonic compressor cascade and a transonic turbine cascade were adopted as model cases.In the experiment, the unsteady aerodynamic force acting on the blade was measured by the influence coefficient method. Behavior of the blade boundary layer was detected with the output signal from hot-film sensors attached to the blade surfaces.From the results on the compressor cascade, the unsteady behavior of the separation bubble on the oscillating blade was clearly shown, and its influence on the unsteady aerodynamic force I moment was revealed.In the experiment on the transonic turbine, the effect of shock wave oscillation on the blade vibration was found quite important. The shock-boundary layer interaction induced a rapid development of the suction-surface boundary layer as well as the boundary layer separation. A remarkable instability of the blade oscillation was detected in the case of low frequency oscillation.A numerical method for unsteady flow around oscillating blades was developed by which the 2D Navier-Stokes equations including Baldwin-Lomax turbulence model were solved with a TVD scheme. The method was verified to be useful through the comparison of the results with available experimental data.A numerical simulation on the transonic turbine was performed on the assumption of inviscid flow. The mechanism of the vibration instability found in the experiment was investigated in detail with the numerical result. It was revealed that the significant phase change around the shock impingement point on the blade suction surface was the dominant factor of the instability.